1. Field of the Invention
The present invention relates to a spread illuminating apparatus, and more particularly to a spread illuminating apparatus used as an illuminating means for a liquid crystal display.
2. Description of the Related Art
A liquid crystal display which is low in profile, small in occupied volume and lightweight has been extensively used in electric products including portable telephones and personal computers, and its demand has been increased. However, since a liquid crystal which is a component of the liquid crystal display does not emit light by itself, it is necessary to provide a separate illuminating apparatus besides the liquid crystal display when used in dark places where the solar light or the illumination in a room is not fully available. Thus, this illuminating apparatus which irradiates liquid crystals is desired to be compact and small in power consumption. And, in recent years, a low profile spread illuminating apparatus of side light system (light conductive plate system) is often used as the illuminating means.
FIGS. 5 to 9 show an embodiment of such a spread illuminating apparatus of side light system.
FIG. 5 is a perspective view showing the spread illuminating apparatus. As shown in the figure, a spread illuminating apparatus 1xe2x80x2 generally comprises a transparent substrate (a guide plate) 2 made of a light-transmissible material, and a bar-like light source 5 disposed close to an end surface 8 of the transparent substrate 2. A liquid crystal display (not shown) is disposed under the transparent substrate 2, and this spread illuminating apparatus 1xe2x80x2 is used to auxiliarily illuminate the liquid crystal display.
The light source 5 comprises a bar-like light conductive member (guide rod) 3 made of a transparent material and disposed along and close to the end surface 8 of the transparent substrate 2, and spot-like light sources (for example, LED) 4a and 4b disposed facing respectively ends 10 and 11 of the light conductive member 3. The spot-like light sources 4a and 4b are mounted and soldered on a flexible printed circuit board (FPC) 6xe2x80x2 formed of an insulating material.
Since an optical path conversion means 12 (comprising grooves substantially triangular in section and flat portions formed therebetween) is provided on a surface of the light conductive member 3 opposing a surface 9 facing the transparent substrate 2, light emitted from the spot-like light sources 4a and 4b is adapted to enter the end surface 8 of the transparent substrate 2 in a substantially uniform manner.
The transparent substrate 2 is formed in a so-called wedge-shape in section in such a manner that the thickness thereof gradually decreases with the increase in distance from the end surface 8. A light reflection pattern 19 comprising grooves 17 and flat portions 18 is formed on an upper surface 15 of the transparent substrate 2, and in this configuration, light coming from the light source 5 and guided into the transparent substrate 2 is reflected in such a manner that an illumination is substantially uniform at the transparent substrate 2 irrespective of the distance from the light conductive member 3.
For allowing light emitted from the spot-like light sources 4a and 4b to efficiently enter the transparent substrate 2, a light reflection member (reflector) 13 is provided around the light conductive member 3. The light reflection member 13 is formed to be substantially square U-shaped, and mounted to longitudinally cover the surfaces of the light conductive member 3 except for the surface 9 facing the transparent substrate 2. The light reflection member 13 is formed of a hard resin having a film vapor-deposited with a metal such as silver, or a white film adhered on its inner surface, or a bent metal sheet of aluminum, stainless steel or the like.
FIGS. 6 and 7 illustrate the light source 5 showing a surface of the light conductive member 3, on which the optical path conversion means 12 is formed. FIG. 6 shows a view before the light conductive member 3 is fitted between the spot-like light sources 4a and 4b, and FIG. 7 shows a view after the light conductive member 3 is fitted therebetween FIG. 8 shows a top plan view of the light conductive member shown in FIG. 7.
The spot-like light sources 4a and 4b are disposed facing the ends 10 and 11, respectively, of the light conductive member 3, and ends 21a and 21axe2x80x2, and 21b and 21bxe2x80x2 of the respective spot-like light sources 4a and 4b are soldered (hereinafter, a part which is soldered is referred to as xe2x80x9csoldering part Sxe2x80x9d) on the FPC 6xe2x80x2, whereby the spot-like light sources are electrically connected to a signal pattern (not shown) formed on the FPC 6xe2x80x2.
The FPC 6xe2x80x2 is substantially rectangular, and disposed under the spot-like light sources 4a and 4b and the light conductive member 3 disposed between the spot-like light sources 4a and 4b. 
The light conductive member 3 is disposed so that the ends 10 and 11 face the spot-like light sources 4a and 4b, respectively, namely, disposed so as to be sandwiched between the two spot-like light sources 4a and 4b mounted on the FPC 6xe2x80x2. The surface 9 of the light conductive member 3 is positioned along the end surface 8 of the transparent substrate 2 with a predetermined distance from the end surface 8.
To obtain excellent optical characteristics in the spread illuminating apparatus, it is required that the light conductive member and the LED""s be tightly attached to each other while securely positioned, and that the coupling efficiency therebetween be satisfactory. However, in the conventional art, marginal spaces between the spot-like light sources 4a and 4b and the light conductive member 3 are necessary in order to smoothly fit the light conductive member 3 between the spot-like light sources 4a and 4b mounted on the FPC 6xe2x80x2. The marginal spaces are necessary also for absorbing tolerances of members to be used (the light conductive member, the spot-like light sources, the FPC, etc.). Further, a positional error in mounting the spot-like light sources 4a and 4b on the FPC 6xe2x80x2 should be also considered. Thus, as shown in FIG. 9 (a blown-up view of Part P in FIG. 7), a space 22 may exist between the light conductive member 3 and the spot-like light source 4a when the light conductive member 3 is placed between the spot-like light sources 4a and 4b, which degrades a coupling efficiency between both components.
The present invention has been made in light of the above problem. Accordingly, it is an object of the present invention to provide a spread illuminating apparatus to improve the coupling efficiency between a light conductive member and a spot-like light source.
In order to solve the above problem, according to a first aspect of the present invention, in a spread illuminating apparatus comprising a transparent substrate made of a light-transmissible material, a light source comprising a bar-like light conductive member and spot-like light sources provided at respective ends of the light conductive member, and disposed close to and along an end surface of the transparent substrate, and a flexible printed circuit board (FPC) disposed under the light conductive member, a portion to generate an elastic force in the longitudinal direction of the light source is formed in the FPC which has the spot-like sources mounted thereon and disposed at the respective ends of the light conductive member.
In the present invention, the light conductive member disposed between the spot-like light sources mounted on the FPC is surely fixed by the elastic force generated in the FPC and working in the longitudinal direction of the light source.
According to a second aspect of the present invention, in the spread illuminating apparatus according to the first aspect of the present invention, the portion generating the elastic force is formed such that the FPC has a deformation between the spot-like light sources.
According to a third aspect of the present invention, in the spread illuminating apparatus according to the first or second aspects of the present invention, the deformation of the FPC is U-shaped. Since the FPC is U-shaped, the elastic force in the FPC is given in the longitudinal direction of the light source so as to work toward the spot-like light sources, spaces between the respective spot-like light sources and the light conductive member disposed therebetween can be reduced, and the coupling efficiency between these components is improved.
According to a fourth aspect of the present invention, in the spread illuminating apparatus according to any one of the first to third aspects of the present invention, a wiring pattern of the FPC is designed so that the distance between the spot-like light sources mounted on the FPC is smaller than the length of the light conductive member.
With such a design, an elastic force working in the longitudinal direction of the light conductive member can be generated in the FPC when the light conductive member is fitted between the spot-like light sources, and a positional error in mounting the spot-like light sources on the FPC can be absorbed, whereby the spaces between the respective spot-like light sources and the light conductive member are reduced or eliminated, improving the coupling efficiency between these components.